The present invention relates to a method for fabricating a semiconductor device, and more particularly to a method for forming a tungsten layer and a method for forming a tungsten wiring layer in a semiconductor device.
The refresh function for a volatile memory device, such as a dynamic random access memory (DRAM) consumes a large amount of electric power. As a result, the refresh process can be a problem for mobile products. Consequently, this problem can be solved by increasing the refresh cycle. A possible solution for increasing the refresh cycle is to decrease parasitic capacitance (Cb) in the cell.
When the thickness of a bit line conduction layer, i.e., a tungsten layer, is reduced, the parasitic capacitance (Cb) is decreased. However, excessive thickness reduction of the bit line increases sheet resistance of the bit line, which decreases the operating speed of the semiconductor device. In order to solve this problem, research has been conducted on a process for forming a tungsten layer having low resistivity. One representative example is a method of forming a tungsten nucleation layer using a diborane (B2H6) gas. Specifically, the tungsten nucleation layer is formed by atomic layer deposition (ALD) through successive actions of the diborane (B2H6) gas and a tungsten hexafluoride (WF6) gas, then the tungsten layer is deposited by hydrogen reduction. As a result, the grain number of the tungsten is increased, which decreases the scattering due to grain boundary, thus lowering the resistivity of the tungsten layer.
However, the excessive use of the diborane (B2H6) gas causes boron (B) to remain in the tungsten layer. As a result, the leakage of current is increased due to the permeation of the boron (B) into the joint area, the characteristics of the semiconductor device are deteriorated, and the yield of the semiconductor device is decreased.